So now that we're familiar with how monosaccharide cyclize, in this video we're going to introduce anomers. So monosaccharide cyclization also generates alpha and beta anomers, but what in the world are animers? Well, animers are literally defined as cyclic sugars that differ only in the configurations of their anomeric carbons. And recall from our previous lesson videos, we already know that the anomeric carbon is the only ring carbon that's attached to 2 oxygen atoms and the anomeric carbon can also be defined as the carbon atom that used to be the carbonyl carbon before cyclization. Now we know from our previous lesson videos that upon monosaccharide cyclization, the anomeric carbon is formed and the anomeric carbon becomes part of either a hemiacetal or a hemiketal. But what we have not yet mentioned is that upon monosaccharide cyclization, the anomeric carbon becomes a chirality center, and that means that it's going to have 2 possible configurations. The first is the alpha configuration and the second is the beta configuration. And so, this is what leads to the alpha anomer and the beta anomer depending on the configuration of the anomeric carbon. So before we actually define the alpha and beta anomers, let's take a look down below at our image and notice over here on the far left we're starting with a linear or an open chain sugar, D glucose, which notice has an aldehyde group up here on carbon number 1 and it has this highlighted hydroxyl group here on carbon number 5. And we've got our muscle man here bending our linear glucose so that these 2 groups are in close proximity. So notice the hydroxyl group here on C5 is in close proximity to the aldehyde group here on carbon number 1 and we know from our previous lesson videos that the alcohol group is going to act as a nucleophile and attack this carbonyl group But this alcohol group can actually attack this carbonyl group in 2 different ways. And that's what leads to these 2 different pathways and these 2 different results that we see here. And so, this alcohol group can either attack the carbonyl group from the top side of the carbonyl or it could attack from the bottom side of the carbonyl. And so, if the alcohol group attacks from the top side, then what we'll get is this anomer that we see here which is the alpha anomer or alpha D Glucopyranose. And so what exactly is this alpha anomer? Well, this is gonna be when the anomeric carbon's hydroxyl group is on the opposite side of its highest numbered carbon. And so when we take a look at this alpha anomer down below, notice that its anomeric carbon is this c one carbon here. And notice that its alcohol group is going down below the plane of this ring here. It's pointing in a downwards fashion and notice that the highest numbered carbon atom is carbon number 6 here and carbon number 6 is pointing in an upwards fashion. And so we have carbon number 6 pointing upwards and we have the alcohol group of the anomeric carbon pointing downwards. And so they are pointing in these, opposite, directions. And so, what you can see is that, with alpha here, the hydroxyl groups, is of the anomeric carbon is reaching down for the ants and so you can think alpha is reaching down for the ants, the tiny little ants that are crawling on the floor and so that's what helps me remember the alpha anomer. Now, on the other hand, if this hydroxyl group doesn't attack from the top, instead, it attacks from the bottom, then what we'll get is this other anomer over here and this is the beta anomer or beta D Glucopyranose in this case. And so, of course, the beta anomer is going to be when the anomeric carbons hydroxyl group, instead of being on the opposite side, it's now going to be on the same side, of its highest numbered carbon. And so what you'll notice is this time the hydroxyl group is going upwards. It's going up in this direction instead of going down like what it was before. And that means that it's pointing in the same direction as the highest numbered carbon, carbon number 6. And so what you'll see is that carbon number 6 and the hydroxyl group are both on the same side. And so what helps me remember that the beta confirmation is on the same side is that when you go and write beta, notice that the two bumps of this beta are on the same side as this pole here. And so as silly as that might sound, that'll help you remember that when these two groups are pointing on the same side of the ring, that it will be a beta confirmation. And so, one thing to point out here is that, these 2 anomers, the alpha anomer and, the beta anomer down below, these anomers are absolutely not mirror images of one another. And so as close as they might seem, they're not mirror images which is why we have this broken mirror here to remind you of that. And, again, you can see that this alcohol group of the anomeric carbon is reaching down for the ants. So it's gonna be the alpha, form. And, this, alcohol group of the anomeric carbon is on the same side as the highest numbered carbon. So it's going to be in the beta form. And so, it's important to be able to distinguish and recognize these 2 different anomers that can exist for, cyclic sugars. And so that concludes our introduction to anomers and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you guys in our next video.
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example
Anomer Example 1
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Video transcript
Alright. So here we have an example problem that's asking which of the following molecules are anomers? And we've got these 5 potential answer options down below. Now recall from our last lesson video that animers are literally cyclic sugars that are identical in every single way except for the configuration of the anomeric carbon. And so when we took a look at option a, comparing molecule 1 with molecule 2, of course, we're gonna be comparing the anomeric carbons first. And so recall that the anomeric carbon is going to be the only carbon atom that is bound to 2 oxygen atoms. And so for sugar 1, the anomeric carbon is this carbon here. And for sugar 2, the anomeric carbon is this carbon here. And so notice that the alcohol group on the anomeric carbon is pointing in the same direction away from the highest numbered carbon. And so what that means is that both of these are reaching down for the ants and so they're gonna both be in the alpha configuration. But for them to be animers, they have to have opposite configurations. So these 2 are not going to be animers of each other. So we can go ahead and cross off option a. And while we're looking at molecule number 1, might as well move on to option c, which is also looking at molecule 1 and comparing molecule 1 to molecule 5. And this time, when we look at the anomeric carbons of both of these sugars, notice that they're going in opposite directions. That sugar 1 is in the alpha configuration as we already indicated and sugar 5 alcohol group on the anomeric carbon is going in the same direction as the highest number carbon making a beta configuration. So right, so far in comparing these 2, they seem to be animals. But remember, this must be the only way that these two sugars differ from each other for them to be considered animals. But notice that these two sugars differ from each other in more than just the configuration that we've already noted. Notice that this carbon over here has its hydroxyl going up, whereas this carbon here has its hydroxyl going down. So these two carbons differ from each other than more than just the configuration of the anomeric carbon which means that they are not going to be animals of each other and we can go ahead and cross off option C. And again, while we're looking at molecule 1, might as well move on to option E here which compares molecule 1 to molecule 4. And notice that molecule 1 is a pyronose with a 6 membered ring, whereas molecule 4 is a furanos with a 5 membered ring. So already, there's no way that these 2 can be animers of each other. So, we can go ahead and cross off option E. So, now, we're between either option B or option D and notice option d comparing molecule 3 here to molecule 4. When we look at the anomeric carbons, notice the anomeric carbon is here and here. Notice that they both have the same configuration of beta And so, again, for them to be anomers, they have to have opposite configuration. So they have the same configuration and, that means that they are not going to be anomers, which of course leaves us with option b, molecule 2, and molecule 5. And so looking at molecule 2 and molecule 5, notice, that their anomeric carbons are in opposite configurations, that this one is reaching down for the ants, so it's gonna be alpha and, this one here is reaching up, to the same side as the highest number carbon. So, same side is gonna be beta. So, when we compare the rest of, both of these molecules, so the rest of this and the rest of this are identical to each other. And so the only way that these 2 differ from each other is in the configuration of the anomeric carbon and that's what makes them anomers. So, we can go ahead and indicate that the correct answer for this problem is option b. And, that concludes this practice problem. So I'll see you guys in our next video.
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Problem
Problem
The ___/___ configuration of a monosaccharide is determined by the ________________ of the chiral carbon furthest from the carbonyl group, while the ___/___ anomers are determined by _______________ of the anomeric carbon.
A
D ; L ; conformations ; R ; S ; configuration.
B
R ; S ; conformation ; α ; β ; configuration.
C
D ; L ; configuration ; α ; β ; conformation.
D
D ; L ; configuration ; α ; β ; configuration.
E
D ; L ; conformation ; α ; β ; conformation.
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Problem
Problem
Answer the following questions regarding the following cyclic monosaccharide shown below:
A) Clearly label the hemiacetal carbon.
B) The monosaccharide is a(n) _________ anomer. a) Alpha (α). b) Beta (β).
C) Draw the opposite anomer.
D) Draw the α stereoisomer that differs in the arrangement of substituents at C2.